The present invention relates to devices for the fixation and/or support of bones. In particular, the present invention relates to a bone support assembly, and a corresponding bone support plate, for the fixation and/or support of bones of the spinal column. The plate of the present invention has particular application in situations where compressional or “settling” forces, as well as torsional and flexing forces, of “fixed” vertebrae on a spinal plate cause significant stressing and potential failure of the spinal plate and/or plate components.
Vertebral fixation has become a common approach to treating spinal disorders, fractures, and for fusion of vertebrae at the time such fixation is instituted. Namely, one or more vertebrae are fixed in position relative to one or more other vertebrae above and/or below the vertebrae to be fixed. Generally, a spinal plate is the device of choice used for mechanically supporting such vertebral fixation. A typical spinal plate includes a plate having a plurality of apertures therethrough. A corresponding plurality of fasteners, i.e., bone screws, are generally positioned into and through respective apertures of the plate to secure the spinal plate to a bone, such as two respective upper and lower supporting adjacent spinal vertebrae. The screws are fastened to the respective support vertebrae to secure the spinal plate to the respective vertebrae. In general, such plate and screw assemblies can be utilized, generally, for anterior fixation of the spine for cervical, lumbar, and/or thoracic fixation.
The basis of anterior fixation or plating is to approach the spine from an anterior or anterio-lateral approach, and use the screws to solidly mount the spinal plate to the affected vertebrae. Often, in addition to the application of a spinal plate, graft material may be combined in an attempt to permanently fuse together adjacent vertebrae. The graft material can consist of bone grafts obtained from bones of the recipient or another individual.
A common problem associated with the use of such spinal plates is the tendency of the bone screws to “back out” or pull away or withdraw from the bone into which they are fixed. This problem occurs, primarily, due to the normal torsional and bending motions of the body and spine. This is a particularly important problem because as the screws become loose and pull away or withdraw from the bone, the heads of the screws can rise above the surface of the spinal plate and, possibly, even work their way completely out of the bone. While this condition can cause extreme discomfort for the recipient, this condition can also create a number of potentially serious physiological problems given the significant amount of nervous and vascular structures associated at or near the potential locations of anterior spinal plate fixations.
A number of designs have been proposed in attempts to prevent screws from pulling away or withdrawing from the bone and/or to prevent the screws from backing out or pulling away or withdrawing from the surface of the spinal plate. Such mechanisms used to prevent bone screws from pulling out of bones include cams which engage and lock the screws, and the use of expanding head screws which expand outwardly when adequate force is applied thereto to engage the holes in the spinal plate. All of these designs have detriments including potential for breakage or requiring particular precision and alignment in their application in order to work correctly. Additionally, loose components and accessories of spinal plates which address the “backing-out” or withdrawal problem can get dropped and/or misplaced while the vertebral fixation surgical procedure is taking place, prolonging and complicating the procedure as well as creating substantial risk of harm to the recipient.
Yet another common problem associated with the use of such spinal plates is the tendency of the vertebrae being “fixed” to settle after spinal plate insertion adding compression forces to the above-listed forces which cause the bone screws to “back out” or pull away or withdraw from the bone into which they were fixed.
It is an object of the invention to provide bone support assemblies which provide rigid bone-to-bone fixation and/or support, such as e.g. adjacent or second adjacent vertebrae, while allowing post-procedural compression between the respective bones.
It is another object of the invention to provide bone support assemblies which afford substantial protection against pulling away or withdrawal of affixing components which may result from torsional movement, flexing movement, or stress and/or dynamic load sharing of the vertebrae, thereby enhancing the bone rebuilding process.
It is yet another object of the invention to provide bone support assemblies which attenuate application of stress on the apparatus and affixing components.
It is a further object of the invention to provide bone support assemblies comprising a bone support plate and resiliently flexible bands so mounted and positioned to enable bone fasteners to pass such bands, with corresponding flexing or other movement of such bands, when the bone fasteners are being installed in a recipient and which, in combination with the designs of the bone fasteners, prevent withdrawal of such bone fasteners after installation in the recipient.
It is yet a further object of the invention to provide bone support assemblies which can be completely pre-assembled such that no assembly steps need be performed on the bone support assembly, itself, while the bone support assembly is being installed in a recipient thereof.
It is still a further object of the invention to provide bone support assemblies wherein apparatus, in such bone support assemblies, for preventing withdrawal of bone fasteners from the bone, after installation on a recipient, are automatically activated, to prevent such withdrawal, as a consequence of the installation of suitably-configured such bone fasteners.